Use of electromagnetic pulses in cross-flow filtration systems

ABSTRACT

A cross-flow filtration system includes a first filter element having a first conduit for receiving a flow of a first aqueous feed stream, a second conduit operable to discharge a flow of first permeate water and a third conduit operable to discharge a flow of first retentate water. The cross-flow filtration system includes a coil assembly disposed about the first conduit. The first coil assembly is operable to subject the first aqueous feed stream to electromagnetic pulses. A second filter element is in fluid communication with the first filter element via the third conduit. The second filter element is operable to receive the first retentate water via the third conduit. A second coil assembly is disposed about the third conduit and is operable to subject the first retentate water to electromagnet pulses.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of commonly owned U.S. patentapplication Ser. No. 11/900,094, entitled “Use of Electromagnetic Pulsesin Cross-Flow Filtration Systems,” filed Sep. 7, 2007, the entirety ofwhich is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to filtration systems and, in particular, tocross-flow filtration systems.

BACKGROUND

Filtration is a process in which contaminants in a fluid such as water,for example, particulate matter and, in some cases, dissolved species,are removed from the fluid by flowing the contaminated fluid through afilter membrane. Filtration exists in two basic forms, dead-endfiltration or cross-flow filtration. Typically, in dead-end filtration,all of the liquid fed to the filter membrane (the “feed stream”) mustpass through the filter membrane and all the filtered material must beretained by the filter membrane. A drip-type coffee maker, in whichground coffee is placed in a basket which has been lined with a filtermembrane of porous paper, provides an example of dead-end particulatefiltration. Hot water is poured onto the coffee grounds in the basket toconstitute a feed stream for the filter. As the water passes through thecoffee grounds, it dissolves the soluble components of the coffeegrounds. The water and the soluble components therein pass through thefilter membrane, while the insoluble components of the coffee remain inparticulate form and are retained by the filter membrane. Filtration ofthis type has practical limits on the size of the particulate matterwhich can be removed and the amount of power (alternatively, rate offiltration) required to process a given amount of feed stream material.

Cross-flow filtration differs from dead-end filtration in that not allthe fluid of the feed stream passes through the filter membrane and notall the contaminants are retained on the filter membrane. In cross-flowfiltration, the feed stream of contaminated fluid is flowed along asurface of a filter membrane that is permeable to the fluid butimpermeable to one or more contaminants in the fluid. Some of the fluidpasses through the filter membrane, which removes some of thecontaminants so that the fluid that emerges is purified. This purifiedfluid is called “permeate” or “product”. The remaining fluid by-passesthe filter membrane, carrying contaminants with it, and exits withoutbeing filtered. This material is called “retentate” or “reject” or“concentrate.” The continual motion of fluid across the surface of thefilter membrane causes some of the contaminant material to be removedfrom the filter membrane and to exit with the reject. The filtermembrane is normally packaged in a flow-through vessel to provide afilter element to which a feed stream is provided and from whichpermeate and retentate are collected.

Cross-flow filtration can be used to filter smaller particles than ispractical with dead-end filtration. Four general classes of cross-flowfiltration are known in the art: microfiltration, ultrafiltration,nanofiltration and reverse osmosis. Each of these classes of filtrationmakes use of a semi-permeable filter membrane (sometimes also referredto herein simply as a “filter” or as a “membrane”). Cross-flow filtermembranes are sometimes classified as low-pressure membranes (whichinclude microfiltration membranes and ultrafiltration membranes) andhigh-pressure membranes (which include nanofiltration membranes andreverse osmosis membranes). Low-pressure membranes filter particulatesincluding organisms such as bacteria and viruses. Nanofiltrationmembranes filter particulates and some larger ions. Reverse osmosismembranes filter particulates and a wider range of ions than doesnanofiltration.

Each form of cross-flow filtration suffers from one or more problemswhich limit productivity. The “flux,” or productivity, of a membrane,i.e., the volume of water which may be processed by a membrane,decreases with increasing fouling. Fouling may consist ofinorganic/scale, particulate/colloidal, microbial, or organic depositsthat accumulate on the membrane. The productivity of a low-pressuremembrane can be limited by the growth of biological material (biofilm)on the membrane and the filterability of particulate matter. Thefilterability of the particulate matter is a function of the size of theparticles and the degree to which they deform or pack as they arefiltered. Large, hard, non-deforming particles are more easily retainedby most filters without clogging than are small, sticky particles. Ingeneral, biofilm is the result of bacterial growth on surfaces,including the surfaces of filter membranes. A common problem forlow-pressure membranes is that the fluid to be filtered (commonly,water) contains both bacteria and nutrients for the bacteria. Thebacteria settle on the membrane and secrete a polysaccharide binder orglue. The presence of this film significantly reduces the permeabilityof the biologically coated membrane. Low-pressure membranes can bebackwashed if they become clogged with particulates or similarcontaminants.

Typically, a high-pressure membrane is mounted on, and wound around, aperforated product collection tube. The wound membrane-productcollection tube assembly is mounted in a pressure vessel to yield afilter element. The pressure vessel has an input where a feed stream isflowed under pressure into contact with the membrane, and two outputs,one output being the product collection tube (where permeate iscollected) and the other being a collection tube for fluid containingthe contaminants that did not pass through the membrane (where retentateis collected). The filter element is constructed such that only thepermeate can enter the product collection tube.

Most high-pressure membranes are packaged (wound) so that the spacesthrough which the fluid to be filtered must pass are very small. Inaddition, high-pressure membranes cannot be backwashed and must beprotected from most if not all particulate matter by pretreatment steps.For example, it is common practice to provide pretreatment of feedstream water in a reverse osmosis system, to remove most of theparticulate matter before the water passes to the reverse osmosis filterelement. The pretreatment can be in the form of conventional filtration(sand filter, coagulant addition, settling) or in the form of alow-pressure membrane (with the inherent limitations described above).Pretreatment for a reverse osmosis system may also include pH regulationof the feed stream.

Despite such pretreatment, high-pressure membranes have performancelimiting problems. The two primary fouling problems for high-pressuremembranes are biofilm and scaling. The biofilm problem is as previouslydescribed for low-pressure membranes. Addressing biological problems inhigh-pressure membranes are more difficult than it is in low-pressuremembranes because the spaces in which the biofilm grows are smaller,making plugging with live or dead bacteria more of a concern, andbecause high-pressure membranes are quite sensitive to biocides such aschlorine.

Scaling is a problem which can occur in nanofiltration membranes butwhich is much more prevalent in reverse osmosis membranes. In theprocess of reverse osmosis, water containing some very fine particulatesand ions (e.g., Ca⁺², Na⁺, Mg⁺²′ Cl⁻, CO₃ ⁻², SO₄ ⁻²) is passed along afirst side of a membrane. As the feed stream water to be filtered passesalong the membrane, some of the feed stream passes through the membraneand is emitted from a second side of the membrane as pure water (i.e.,water that is substantially free of ions). This process causes the ionswhich remain on the first side of the membrane to increase inconcentration in the remaining water, generating retentate. Ifsufficient water is allowed to pass through the membrane, the remainingsolution (the retentate) will reach saturation for some of the ionspresent and minerals (e.g., CaCO₃ and or CaSO₄) will precipitate. Thisprecipitate will inhibit, and may preclude, the further passage of waterthrough the membrane. The need to avoid scaling limits the percentage ofpure water which can be recovered from the feed stream.

A typical reverse osmosis filter element will yield about 50% permeateliquid, and 50% concentrate liquid. For example, if 100 gallons perminute (GPM) of liquid is fed into a reverse osmosis system,approximately 50 GPM of permeate will be output, and 50 GPM ofconcentrate or retentate will also be output.

A reverse osmosis system may have several stages wherein the retentatefrom one filter element (the first stage) is processed by a subsequentfilter element (a second stage), and so on. In general, a maximumrecovery from the initial feed stream is about 85% converted topermeate. Accordingly, when 100 million gallons of feed liquid isprocessed through the stages of a reverse osmosis system, approximately15 million gallons of retentate will be generated and must be properlydisposed of.

As noted above, after a period of operation, a reverse osmosis membranecan become fouled with mineral scale and/or bacteria that diminish thefiltration performance of the membrane. Bacteria contribute to theformation of a biofilm that further diminishes the performance of themembrane. Typically, when a membrane in a reverse osmosis system becomesfouled to an unacceptable level, the membrane must be removed from useto be cleaned. However, each time a membrane is cleaned, itseffectiveness and production capacity is reduced.

SUMMARY OF THE INVENTION

The present invention resides in one aspect in a method of treating aliquid feed stream by flowing the feed stream to a cross-flow systemcomprising a first filter element, to yield a first permeate and a firstretentate, and subjecting the feed stream to electromagnetic pulses. Ina particular embodiment, the invention is practiced on the feed streamof a reverse osmosis filtration process.

The present invention resides in another aspect in a cross-flowfiltration system comprising a filter element having an input feed pipefor receiving a flow of feed stream fluid. The filter element yields aflow of permeate and a flow of retentate. A coil assembly is disposedabout the input feed pipe, for subjecting the feed stream toelectromagnetic pulses.

In another aspect of the present invention there is disclosed across-flow filtration system that includes a first filter element havinga first conduit for receiving a flow of a first aqueous feed stream, asecond conduit operable to discharge a flow of first permeate water anda third conduit operable to discharge a flow of first retentate water.The cross-flow filtration system includes a coil assembly disposed aboutthe first conduit. The first coil assembly is operable to subject thefirst aqueous feed stream to electromagnetic pulses. A second filterelement is in fluid communication with the first filter element via thethird conduit. The second filter element is operable to receive thefirst retentate water via the third conduit. A second coil assembly isdisposed about the third conduit and is operable to subject the firstretentate water to electromagnet pulses.

In another aspect of the present invention there is disclosed across-flow filtration system including a first filter element having afirst conduit for receiving a flow of a first aqueous feed stream, asecond conduit operable to discharge a flow of first permeate water anda third conduit operable to discharge a flow of first retentate water.The cross-flow filtration system includes a first coil assembly disposedabout the first conduit. The first coil assembly is operable to subjectthe first aqueous feed stream to first electromagnetic pulses. Thecross-flow filtration system includes a second filter element in fluidcommunication with the first filter element via the third conduit. Thesecond filter is operable to receive the first retentate water via thethird conduit. The second filter element has a fourth conduit operableto discharge a flow of second permeate water and a fifth conduitoperable to discharge a flow of second retentate water. The cross-flowfiltration system includes a third filter element in fluid communicationwith the second filter element via the fifth conduit. The third filterelement is operable to receive the second retentate water via the fifthconduit. The cross-flow filtration system includes one or moreadditional coil assemblies disposed about the third conduit and/or fifthconduit. The additional coil assemblies is/are operable to subject thefirst retentate water to second electromagnet pulses and/or subject thesecond retentate water to third electromagnet pulses.

In a particular embodiment, the coil assembly includes an AC powersource. The AC power source has a period including a first half-cycle ofone polarity and a second half cycle of a polarity opposite to that ofthe first half-cycle. There is a first switch connected in series withthe coil assembly to form a series connected circuit, and a secondswitch connected with the coil assembly to form a second circuit. Thereis also a control means for the first switch. The control means isconfigured to close the first switch and open the second switch during afirst half-cycle of the AC power source period and, during a secondhalf-cycle, to perform a subroutine of closing and then opening thesecond switch to produce at least a first large ringing pulse in thecoil assembly.

Optionally, before the first large ringing pulse substantially decays,the control means closes and opens the second switch to produce a secondlarge ringing pulse. Alternatively, the control means produces a secondlarge ringing pulse after the first large ringing pulse substantiallydecays.

The electromagnetic pulses will aid in minimizing fouling of membraneswhich constitute part of a cross-flow filtration system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram of an apparatus for generating aringing electromagnetic pulse for treating flowing liquid in accordancewith the invention;

FIG. 2 is an oscilloscope trace showing a single large ringing pulseaccording to the invention;

FIG. 3 is an oscilloscope trace showing a “natural” ringing pulsefollowed by more than one large ringing pulse according to theinvention;

FIG. 4 is an oscilloscope trace showing a series of six full largeringing pulses according to the invention; and

FIG. 5 is an oscilloscope trace showing a series of ringing pulsesinitiated without letting prior pulses substantially decay, according toone embodiment of the invention; and

FIG. 6 is a schematic view of a reverse osmosis element portion of areverse osmosis system that employs electromagnetic pulse treatment asdescribed herein, according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A cross-flow filtration system is improved by flowing a feed stream ofcontaminated fluid to a cross-flow filter element, and subjecting thefeed stream to pulses of electromagnetic radiation as described herein.As a result of such treatment, fouling of the filter membrane in thefilter element will be diminished, and the operational output of thefilter membrane and its useful life will be extended. Thus,electromagnetic pulse treatment as described herein improves efficiencyand reduces costs associated with membrane cleaning and replacement. Asused herein, the term “feed stream” refers to a stream of fluid that isflowed into a first side of a filter membrane so that fluid may passthrough the filter membrane and be released from the second side toyield permeate. The invention can be practiced with a cross-flow filterelement for any kind of cross-flow filtration: microfiltration,ultrafiltration, nanofiltration, or reverse osmosis.

The invention may be employed in cross-flow filtration systemsconfigured to provide multiple stages of filter elements in successivestaged relation to each other. In such systems, an initial feed streamof contaminated fluid is flowed into a first filter element thatprovides a first filtration stage, yielding a flow of first stagepermeate and a flow of first stage retentate. The first stage retentatebecomes a feed stream to a second filtration stage, producing a flow ofsecond stage permeate and a flow of second stage retentate. Optionally,the second stage retentate may be treated as a feed stream for a thirdfiltration stage, yielding a flow of third stage permeate and thirdstage retentate. Any one or more of the staged feed steams may betreated with electromagnetic pulses as described herein.

The invention may also be employed in a cross-flow filtration systemconfigured to provide multiple passes of permeate through filterelements. In such systems, an initial feed stream of contaminated fluidis flowed into a first filter element that provides a first filtrationpass, yielding a flow of first pass permeate and a flow of first passretentate. The first pass permeate of a first filtration element isflowed as a second feed stream to a second filter element to furtherpurify the first permeate, and to yield a second pass permeate.Optionally, the second pass permeate may be flowed as a third feedstream to a third filter element. Any one or more of the feed steams maybe treated with electromagnetic pulses as described herein.

While filtration systems having three stages or passes are describedherein, the present invention is not limited in this regard as anynumber of stages or passes can be employed without departing from thebroader aspects of the present invention.

Some cross-flow filtration systems may employ both multi-stage andmulti-pass configurations.

While some of the following description refers specifically to a reverseosmosis system, the invention is not limited in this regard.Electromagnetic pulse treatment can be provided in reverse osmosissystems designed to reclaim water for drinking purposes, for use inpower plants, etc. It should be understood, however, that the inventioncan be practiced as well with any other type of cross-flow filtrationsystem.

An illustrative reverse osmosis element for a cross-flow filtrationsystem provides 50% recovery, in other words, the volume rate yield(e.g., liters per minute) of permeate is about 50% of the volume rate ofthe feed stream. Accordingly, in a three-stage reverse osmosis systemthat does not employ electromagnetic pulse treatment as describedherein, and that provides an initial feed stream of 100 gallons perminute (gal/min)(about 6.3 liters per second (l/s)), the first stageyields about 50 gal/min (about 3.15 l/s) product and about 50 gal/minretentate. The second stage, which receives the about 50 gal/minretentate as a feed stream, yields about 25 gal/min (about 1.571 l/s)product and about 25 gal/min retentate. The third stage, which receivesthe about 25 gal/min second stage retentate as a feed stream, yieldsabout 12.5 gal/min (about 0.81/s) product and about 12.5 gal/minretentate. The maximum expected recovery (i.e., the expected maximumaccumulated permeate) is therefore about 87.5% of the initial feedstream; actual yields of about 83% are attained.

In multi-stage reverse osmosis systems that do not employelectromagnetic pulse treatment as described herein, fouling and scalingoccurs in the reverse osmosis elements. In some cases, fouling ispredominant the first stage, while scaling is more prevalent in laterstages. Fouling and scaling reduce the yield rate of the filter elementsand of the system in which the elements are employed. Electromagneticpulse treatment as described herein may be provided at various points ina multi-stage reverse osmosis system, to forestall fouling and scalingand the associated reduction in yield rate. The effect of theelectromagnetic pulse treatment may differ at different stages. Forexample, providing electromagnetic pulse treatment in advance of thefirst stage of a multi-stage reverse osmosis system is expectedprincipally to reduce fouling at the first stage, whereas providingelectromagnetic pulse treatment after the first stage, for example,between the second and third stages, is expected principally to reducescaling at a second or third stage. It is believed that the reduction inscaling will be attained because the electromagnetic pulse treatment caninitiate precipitation of dissolved solutes in the feed stream, even inthe absence of solids in the feed stream or on the interior surface(i.e., the feed stream surface) of the reverse osmosis membrane. Inaddition to reducing fouling and scaling, the electromagnetic pulsetreatment described herein can in some cases increase the yield of areverse osmosis element.

The invention provides an apparatus and a method for the treatment ofaqueous solutions undergoing cross-flow filtration. Said treatmentincludes one or more of increasing the size and/or consistency ofparticulate matter contained in the solution, impeding the growth ofmicroorganisms such as bacteria, and reducing the tendency for mineralscale such as CaCO₃ and CaSO₄ to form on the filtration membrane. Saidtreatment is the result of the presence of electromagnetic fields in thefluid to be treated. Said fields possess one or more of the followingcharacteristics: a low frequency component (commonly 50 to 60 Hz); ahigh frequency component (commonly 10 to 100 kHz); fields vary instrength and direction with time and position within the treatmentdevice; the high frequency component of the signal is similar in form toa signal produced by a damped LC (inductor capacitor) circuit in whichthe current is rapidly and repeatedly interrupted. Signals of this typeare sometimes called “ringing”. The apparatus which generates thetreating electromagnetic fields generally includes two components, asignal-generating component and a field-generating component. Thesignal-generating component includes electric power regulating devicessuch as transformers and switching devices which range upward incomplexity and sophistication from simple diodes. Field-generationdevices include but are not limited to induction coils and/or metalfoils which act as the plates of a parallel plate capacitor. Theapparatus also includes a means to introduce the fields generated intothe water to be treated. This is accomplished by placing the fieldgeneration devices in close proximity to the water to be treated.

The electric and/or magnetic fields may be used as a part of, or apretreatment for, cross-flow membrane filtration processes to improvethe filterability of the fluid through a reduction of: fluid turbidity,biological activity within the fluid, and the tendency of the fluid toform a scale on the membrane. As a secondary effect of the conditionsresulting from the treatment process, the corrosivity of the treatedfluid to materials of construction may be reduced. The fluids treated bythe invention will normally be contained in, and flowing through, achannel such as a pipe. Alternatively, the fluids can be containedwithin a vessel which may be closed or open to the environment and inwhich the fluid is essentially stagnant, such as a membrane bioreactor.

As disclosed in U.S. Pat. Nos. 5,702,600 and 6,063,267 as well as UnitedStates Patent Application Publication No. US-2007-0051685-A1(application Ser. No. 11/304,348) for “Method and Apparatus for TreatingFluids” and United States Patent Application Publication No.US-2006-0124557-A1 (application Ser. No. 11/192,452) for “System andMethod of Generating a Ringing Magnetic Pulse for the Treatment ofFlowing Liquids,” a series of devices have been developed to limitbacterial growth and the formation of scale in a variety of fluidsystems. All of the foregoing United States patent documents areincorporated herein by reference. Although not discussed in thesedisclosures, the mechanism by which these devices limit the formation ofscale is also believed to cause particulate matter to grow in size and,thereby, become more filterable. Collectively, devices described in theaforementioned patents and applications will be referred to as “pulsedpower devices”. One such device is currently manufactured by ClearwaterSystems Corporation of Essex Conn. and is marketed under the trade name“DOLPHIN™ device.” To date, the primary purpose of the DOLPHIN™ deviceand preceding devices has been the treatment of water in airconditioning cooling towers.

Without wishing to be bound by any particular theory, water treatment bythe DOLPHIN™ device and preceding devices (pulsed power devices) appearsto be the result of the presence of magnetic and electric fields whichvary with time in strength and direction. These fields exist within apipe containing flowing water and result in modifications to theproperties of the treated water which are considered to be beneficial.Aspects of the apparatus and methods of operation of the DOLPHIN™ devicethat are pertinent to the present disclosure are described briefly belowin the context of operation in a cooling tower environment.

To date pulsed power devices have consisted of two primary components:the control panel and the coil pipe assembly. The control panel consistsof components necessary to generate a relatively low voltage (in therange of 11 to 37 volts) 50-60 cycle signal and to rapidly andrepeatedly interrupt that signal, i.e., to switch the signal on and off.The coil pipe assembly consists of a section of pipe, the material anddimensions of which may vary. One or more induction coils are placedcircumferentially around the pipe. These coil(s) may or may not becoupled with one or more capacitors. The coils and any associatedcapacitance are sized so that when the 50-60 cycle signal is interruptedby the components located in the control panel a high voltage (up to 300volts) high frequency (10 to 50 kHz) rapidly decaying signal isgenerated. This signal and its decay rate are the natural responses tothe inductive and capacitive characteristics of the coil(s). Signalgeneration in this manner is commonly known as “ringing” the coil.

As described by Ampere's law (Eq. 1):

B·dl=μ ₀ i  (1)

where:

-   -   B is the magnetic field strength    -   dl is a differential length    -   μ₀ is the permeability constant    -   i is the current        The passage of current through a wire creates a magnetic field        in a circumferential direction around the wire through which the        current passes. In the case of the DOLPHIN™ device where the        current is being carried in a coil, the resulting magnetic field        is directed axially along the pipe in either the plus or minus        direction (depending on the direction of the current). Given        that the current in the wire varies with time, so does the        resulting magnetic field.

As described by Faraday's law (Eq. 2)

$\begin{matrix}{{\oint{E \cdot {l}}} = {- \frac{\Phi_{B}}{t}}} & (2)\end{matrix}$

where:

-   -   E is the electric field    -   dl is a differential length    -   dΦ_(b)/dt is the rate of change of the magnetic flux        A time varying magnetic field, as is created by both the 50-60        Hz and the ringing currents in the DOLPHIN™ device's coil,        creates an electric field that is oriented at right angles to        the magnetic field. Ignoring end effects, the electric field in        an induction coil is circumferential.

Two of the principal actions of the DOLPHIN™ device, the precipitationof calcium carbonate as powder rather than scale, and the control ofbiological activity, are directly ascribed to the existence of the abovedescribed electrical and magnetic fields. Powder precipitation has beenascribed to a reduction or elimination of the surface charge that isnormally present on colloidal particles by the time varying electric andmagnetic fields. The reduction in surface charges substantially reducesor eliminates the electrostatic repulsion between these particles,which, in turn, increases collisions between particles resulting inrapid particle growth and settling (as opposed to scaling on heattransfer surfaces). The control of biological activity has been ascribedto encapsulation of bacteria in the precipitating calcium powder, aspreviously described, and to a direct interaction between the cellmembrane and the electric and magnetic fields. Bacterial cell membranesare known to act as electrical capacitors. When stimulated by electricand/or magnetic fields at the proper frequency, significant disruptionsin the functions of the membranes are known to occur. When power levelsare sufficiently high, as described in U.S. Pat. No. 6,863,805, whichaddresses the subject of cold pasteurization, the cell membranes areknown to rupture by a process called electroporation.

A schematic representation of a multi-stage reverse osmosis system thatemploys electromagnetic pulse treatment as described herein is seen inFIG. 6. Reverse osmosis system 610 comprises a first reverse osmosiselement 612, a second reverse osmosis element 614 and a third reverseosmosis element 616, all disposed in successive, staged relationship toeach other. A conduit 618 is connected to the input of reverse osmosiselement 612 to provide an initial aqueous feed stream to reverse osmosiselement 612. The conduit 618 is equipped with a first electromagneticpulse coil 620 upstream from first reverse osmosis element 612. Thereverse osmosis element 612 yields two outputs via conduits 612 a and612 b. Conduit 612 a carries a flow of permeate from reverse osmosiselement 612 and is connected to a product collection line 621. Conduit612 b carries a flow of retentate from reverse osmosis element 612 andis connected to the input to reverse osmosis element 614, so that theretentate from reverse osmosis element 612 is provided as a feed streamto reverse osmosis element 614. A second electromagnetic pulse coil 622is mounted to conduit 612 b, upstream from reverse osmosis element 614.

Reverse osmosis element 614 yields two outputs at conduit 614 a andconduit 614 b. Conduit 614 a carries a flow of permeate from reverseosmosis element 614 and is connected to the product collection line 621.Conduit 614 b carries a flow of retentate from reverse osmosis element614 and is connected to the input to reverse osmosis element 616, sothat the retentate from reverse osmosis element 614 is provided as afeed stream to reverse osmosis element 616. A third electromagneticpulse coil 624 is mounted on the conduit 614 b, upstream from the thirdreverse osmosis element 616.

The third reverse osmosis element 616 yields two outputs at conduit 616a and conduit 616 b. Conduit 616 a carries a flow permeate from reverseosmosis element 616 and is connected to the product collection line 621.Conduit 616 b is a waste collection conduit to which retentate fromreverse osmosis element 616 flows.

In various embodiments, system 610 may include any single one ofelectromagnetic pulse coils 620, 622 or 624; or a combination of any twoof the electromagnetic pulse coils or, optionally, all threeelectromagnetic pulse coils. As described further below, anelectromagnetic pulse coil may comprise a coil of wire wrapped aroundthe conduit.

In operation, each feed stream is provided to the respective reverseosmosis element under pressure sufficient to yield a flow of permeateand a flow of retentate from the element. Before the conduit 618provides the initial feed stream to the first reverse osmosis element612, the feed stream is pre-treated to remove particulates in apre-treatment system (not shown). The pre-treated feed stream is thenflowed via the conduit 618 to the first reverse osmosis element 612. Thereverse osmosis element 612 separates purified water (the permeate),which is released via conduit 612 a, from water with concentratedcontaminants (the retentate, which may contain particulates, dissolvedions and/or biological contaminants), which is released via conduit 612b. The retentate in conduit 612 b is provided as a feed stream toreverse osmosis element 614.

Reverse osmosis element 614 separates purified water (the permeate),which is released via conduit 614 a, from water with concentrated salts(the retentate), which is released via conduit 614 b. The retentate inconduit 614 b is provided as a feed stream to reverse osmosis element616.

Reverse osmosis element 616 separates purified water (the permeate),which is released via conduit 616 a, from water with concentrated salts(the retentate), which is released via conduit 616 b.

While feed streams are flowing into reverse osmosis element 612, 614and/or 616, at least one electromagnetic pulse coil 620, 622 and/or 624is powered to generate high frequency electromagnetic pulses.

An apparatus that can employ coils such as electromagnetic pulse coil620, 622 and/or 624 to generate electromagnetic pulses suitable toachieve the present invention is disclosed and described below, withreference to FIGS. 1-5.

An apparatus for generating a ringing magnetic pulse for treating feedstreams of flowing contaminated liquids in accordance with the presentinvention is indicated generally in FIG. 1 by the reference number 10.The apparatus 10 comprises an input power transformer 12 having firstand second output terminals 14, 16, a coil assembly 18, an SCR 20, aoptical relay 22, a MOSFET 24 serving as an electronically controlledswitch, a current level switch 26, a peak voltage detector 28, and aprogrammable digital microcontroller 30.

It has been discovered that digital control systems for generating aringing magnetic pulse can be modified in order to be of simplerconstruction and less expensive by substituting a single siliconcontrolled rectifier (SCR) switch for a MOSFET switch assembly. Thissubstitution provides significant benefits in the generation of theringing pulse as well as the low frequency electromagnetic field, bothof which are considered important in the treatment of fluids. SCRs areavailable with higher current ratings and lower losses relative toMOSFETs, and a single device can easily handle the coil current. As aresult of using the SCR where prior art devices employed a MOSFET, theringing pulse and the low frequency electromagnetic field are generatedmore efficiently than in previous devices. However, SCRs cannot beelectronically turned off as a MOSFET can, so that the high voltage“ringing” pulse has to be produced some other way than by interruptingthe coil current pulse, as will be explained more fully below.

Referring again to FIG. 1, the coil assembly 18 (which is provided asany one or more of electromagnetic pulse coil 620, 622 and/or 624),which comprises a coil and is characterized as having an inductance anda capacitance connected in parallel, has a first end coupled to thefirst terminal 14 of the transformer 12. The illustrated capacitance canbe and is herein taken to be comprised solely of the capacitance of thecoil, but in some coils the stray capacitance may be supplemented by adiscrete capacitor connected in parallel with the coil. The SCR 20 has acathode coupled to a second end 31 of the coil assembly 18, and an anodecoupled to the second output terminal 16 of the transformer 12. Asshown, the anode of the SCR 20 is coupled to electrical ground. Theoptical relay 22 serves as an SCR gate switch. As shown in FIG. 1, theoptical relay 22 is a switch that has a first terminal 32 coupled to thegate of the SCR 20 via a gate resistor 34, and a second terminal 36coupled to ground potential. The optical relay 22 includes a lightemitting diode (LED) 38 that when energized to emit light closes theswitch to enable current flow between the first and second terminals 32,36 of the optical relay 22. Thus, the coil assembly 18 and the SCR 20form a series connected circuit in parallel to the power transformer 12,making a first loop. The switch of the optical relay 22 may be anoptical triac or an optical MOSFET.

The microcontroller 30 includes a first output 40 coupled to an anode ofthe LED 38 via a resistor 42, a second output 44 coupled to the currentlevel switch 26, and a third output 46 coupled to the peak voltagedetector 28. The current level switch 26 includes a first output 48coupled to the microcontroller 30, and a second output 50 coupled to thegate of the MOSFET 24. The peak voltage detector 28 includes an output52 coupled to the microcontroller 30. A digitally controlled currentreference potentiometer 54 is coupled to an input of the current levelswitch 26, and is adjustable by the microcontroller 30. A digitallycontrolled voltage reference potentiometer 56 is coupled to the peakvoltage detector 28, and is adjustable by the microcontroller 30.

The MOSFET 24, such as the illustrated n-channel IGFET with substratetied to source, includes a source coupled to ground potential, and adrain coupled to the second end 31 of the coil assembly 18 via a currentsense resistor 58. A high voltage Schottky diode 60 has an anode coupledto the second end 31 of the coil assembly 18 and a cathode coupled to aninput 62 of the peak voltage detector 28.

The apparatus 10 is generally preferably mounted on a printed circuitboard (not shown). However, two components are preferably external tothe printed circuit board (PCB), namely, the coil assembly 18 and thepower transformer 12. The transformer 12 provides a 50-60 Hz AC power topower the coil assembly 18. The main power component on the PCB is theSCR 20 which is preferably heat-sinked and which functions as acontrollable diode. When an ordinary diode is forward-biased (anodevoltage positive with respect to the cathode) it conducts current. Whenan SCR is forward-biased it will not conduct current unless the gate(control) lead is also forward-biased. Both an SCR and an ordinary diodewill block current if they are reverse-biased.

When the SCR gate lead is connected to its anode (via a resistor), theSCR will conduct current when the SCR anode is positive with respect toits cathode. This occurs during the negative voltage half-cycle (asreferenced to the SCR anode which is considered to be circuit ground inFIG. 1). Since the coil assembly 18 is predominantly inductive (withsome small internal resistance) at 60 Hz, negative current will continueto flow for a large portion of the positive voltage half-cycle. When thecurrent drops to zero, the SCR 20 will block positive current flow (fromcathode to anode) as does a diode rectifier. When the SCR 20 turns off,the voltage across the SCR will jump to a positive level during theremainder of the positive voltage half-cycle. It is during this positivevoltage period that the microcontroller 30 generates at least oneringing current and voltage pulse within the coil assembly 18.

A ringing pulse across the coil assembly 18 is created by first closingthe MOSFET solid-state switch 24 for a brief period at any time duringthe positive voltage cycle when the SCR 20 is off. The MOSFET 24 isclosed, or made to conduct, by applying a positive voltage to itscontrol electrode or gate via the current level switch 26. Positivecurrent will build up in the coil assembly 18 while the MOSFET 24 isclosed (the rise time is determined by the value of the current senseresistor 58 and the inductance of the coil assembly 18). When thecurrent level reaches a designated trigger value, the MOSFET switch 24is abruptly opened by the current level switch 26 (the current levelswitch removes the positive voltage from the gate of the MOSFET 24,which causes the MOSFET to become non-conducting). The inductance andcapacitance values of the coil assembly 18 will determine the frequencyof the resulting resonating current flow within the coil and themagnitude of the ringing voltage as viewed across the SCR 20. The decaytime of the ring is determined by the internal resistance of the coilassembly 18.

The gate resistor 34 of the SCR 20 must be disconnected from the anodeof the SCR during the positive voltage period to prevent the SCR fromturning on when ringing pulses are generated—which would quicklyterminate the ring. An optical relay 22 (as shown in FIG. 1) is providedfor this purpose. The optical relay 22 need only be energized prior tothe start of the negative voltage half-cycle. Once current starts toflow in the SCR 20, the optical relay 22 can be de-energized. The SCR 20will continue to conduct until current drops to zero and thecathode-to-anode voltage across the SCR is positive. Interestingly, asmall ringing pulse in the coil assembly 18 occurs when the SCR 20switches off which is caused by the charge stored in the coilcapacitance.

The operation of the apparatus 10 is primarily implemented using theprogrammable digital microcontroller 30 coupled to and aided by the peakvoltage detector 28 and the current level switch 26. The microcontroller30 does not directly interface with the coil assembly 18, the SCR 20 andthe MOSFET 24; nor does the microcontroller directly view the coilvoltage level. The coil voltage is presented to the current level switch26 and the peak voltage detector 28 through the high voltage Schottkydiode 60. The current level switch 26 and the peak voltage detector 28compare the incoming voltage level to a reference voltage level set bythe digitally controlled potentiometers 54, 56, respectively todetermine its action.

The primary function of the peak voltage detector 28 is to compare thelevel of the coil ringing voltage signal to the reference level set bythe digital potentiometer 56 associated with the peak voltage detector.If the peak level exceeds the given reference level, the peak voltagedetector 28 will store that event so that it can be later read by themicrocontroller 30. The stored event is cleared after it is read by themicrocontroller 30. The peak voltage detector 28 is used to determinethat the peak voltage exceeds the minimum desired value and also that itdoes not exceed a maximum value. A secondary function of the peakvoltage detector 28 is to determine the value of the transformer voltageon start-up. The microcontroller 30 needs to know the transformervoltage because the ring signal rides on top of the transformer voltage.The transformer voltage reading is added to the desired ring voltagelevel when the reference voltage is set.

The current level switch 26 controls the MOSFET 24 used to generate thecoil ringing pulse. The microcontroller 30 sends a trigger pulse to thecurrent level switch 26 to initiate a ring. When triggered, the currentlevel switch 26 raises the voltage on the gate lead of the MOSFET 24,thereby turning it on. The “on” resistance of the MOSFET 24 is much lessthan the value of the current sense resistor 58. The MOSFET 24 is held“on” until the voltage at the current sense resistor 58—coil junction(the cathode of the SCR 20) exceeds the reference voltage set by thecurrent reference potentiometer 54 associated with the current levelswitch 26. The value of the resistor 58 and the reference voltage is notas important as ensuring that the current value at which the MOSFET 24turns off is repeatable for a given potentiometer setting. The role ofthe microcontroller 30 is to adjust the potentiometer 54 of the currentlevel switch 26 to achieve the desired voltage level for the coil“ring.” Thus, the microcontroller 30, potentiometer 54 and current levelswitch 26 regulate at least the initial voltage of the ringing currentpulse. Optionally, the microcontroller 30, potentiometer 54 and currentlevel switch 26 are adapted to keep the voltage of the ringing currentplus between a predetermined minimum value and a predetermined maximumvalue.

The overall operation of the microcontroller 30 is executed in softwareembedded within the microcontroller. The functions of that softwareprogram are now described. When the apparatus 10 is first powered-up,the SCR 20 and the MOSFET 24 are both off (i.e. no current flows throughthe coil assembly 18). The first task of the microcontroller 30 is totest for the presence of coil power voltage from the transformer 12.This can be accomplished by setting the peak voltage detector 28 at alow level and monitoring the output. An alternative method is to monitora tap provided in the current level switch 26 which reads zero when thecoil voltage is negative and rises to +0.5V when the coil voltage goespositive. The microcontroller 30 waits until it observes two alternating50-60 Hz power line voltage cycles before proceeding. When the AC coilvoltage is detected, the microcontroller 30 will measure its peak levelby monitoring the output of the peak voltage detector 28 while it raisesthe level of the voltage reference potentiometer 56. The peak levelreading is retained in the microcontroller 30 and used as an offset foradjusting the level of the generated ring pulses which ride on the coilpower voltage.

The next software task is to turn on the SCR 20, which is a periodictask occurring once per voltage cycle. Since the SCR anode is used asthe ground-reference, the SCR anode-to-cathode voltage is negativeduring the positive voltage portion of the cycle. Just before the end ofthe positive voltage period, the SCR gate switch or optical relay 22 isturned on by powering its optically coupled LED 38. When the negativevoltage across the SCR 20 is approximately 2 volts, the SCR will beginto conduct current, at which time power to the gate switch LED 38 isremoved. The SCR 20 will remain latched on without the gate switch 22being powered, until the SCR 20 current flow drops to zero.

The ringing pulses are produced by a second periodic software task. Thistask waits until the SCR 20 turns off and a positive coil voltage isdetected (which is a sharp jump nearly the height of the peak coilvoltage). The task waits a few milliseconds to allow the small coil ring(which occurs when the SCR 20 turns off) to die out. To generate a highvoltage ringing pulse the software sends a trigger signal to the currentlevel switch 26, which turns on the MOSFET 24, allowing positive currentflow to rise in the coil assembly 18. The task monitors the currentlevel switch 26. When the current level switch signals that the desiredamount of current is present in the circuit, the MOSFET is turned off.The rapid cessation of the flow of current in the coil triggers a largecoil ring.

The microcontroller generates a sequence of large ringing pulses in thesecond half-cycle of the AC power source. The timing of each ringingpulse in a sequence may be timed in relation to the preceding pulse. Forexample, the microcontroller may delay the generation of a subsequentringing pulse for an idle period until the preceding ringing pulsesubstantially decays. For one example of such substantial decay, thegeneration of a subsequent ringing pulse may be delayed at least untilthe magnitude of a preceding pulse decays to about 5% of the initialmagnitude. Following this idle period, the periodic software task isrepeated and a second or subsequent large ringing pulse is generated.The number of pulses which may be generated during each positive voltageperiod depends on the inductance, capacitance, resistance, and voltagein the circuit; 4-6 rings are typical.

In an alternative embodiment, the microcontroller is programmed so thatthe wait time from when the MOSFET 24 is turned off to when the MOSFET24 is turned on again in preparation for generating the next ring isshorter than in the preceding embodiment of the invention. As a resultof this shorter wait period, the generation of significantly greaternumber of rings is possible during each positive voltage period,however, each ring is not permitted to substantially decay as it was inthe first embodiment. For example, a subsequent ringing pulse may begenerated before the preceding ringing pulse decays to about 5%, or toabout 10%, of its initial magnitude. Optionally, a subsequent ringingpulse may be generated before the previous ringing pulse decays to about25%, optionally before the previous ringing pulse decays to about 50% ofits initial magnitude. In some embodiments, a subsequent ringing pulsemay be generated when the magnitude of the preceding pulse decays toabout 10 to about 50% of the initial magnitude. Optionally, a subsequentpulse may be generated when the magnitude of the preceding pulse decaysby about 15 to about 25% of the initial magnitude.

During the negative voltage period, the microcontroller 30 determines ifthe peak voltage detector 28 has been triggered, which indicates thatringing signal exceeded the reference level set in the voltage referencepotentiometer 56. The voltage reference potentiometer 56 can be set toeither the minimum or the maximum desired peak voltage level. If thevoltage reference potentiometer 56 is set for the minimum peak voltage,and the peak voltage detector 28 has not been triggered, themicrocontroller 30 will increase the level of the current referencepotentiometer 54 and leave the voltage reference potentiometer 56 at theminimum level. If the voltage reference potentiometer 56 is set for theminimum peak voltage, and the peak voltage detector 28 has beentriggered, the microcontroller 30 will hold the level of the currentreference potentiometer 54 and change the voltage referencepotentiometer 56 to the maximum level. If the voltage referencepotentiometer 56 is set to the maximum level, and the peak voltagedetector 28 has been triggered, the microcontroller 30 will decrease thelevel of the current reference potentiometer 54 and leave the voltagereference potentiometer 56 at the maximum level. If the voltagereference potentiometer 56 is set to the maximum level, and the peakvoltage detector 28 has not been triggered, the microcontroller 30 willhold the level of the current reference potentiometer 54 and change thevoltage reference potentiometer 56 to the minimum level. The precedingactions will move and hold the peak voltage level for the ring pulsebetween the minimum and maximum desired values. The above logic patternserves as a digital voltage regulator for the ringing voltage pulse.

Also during the negative voltage period, the microcontroller 30 readsthe resistance value of a negative temperature coefficient (NTC)thermistor (not shown) affixed to the heat sink of the SCR 20. If theresistance drops below the value equated to the maximum temperaturedesignated for the SCR heat sink (which is lower than destruction levelfor the SCR 20) the microcontroller 30 will turn off the SCR and alsocease generating ringing pulses. The microcontroller 30 will continue toperiodically read the thermistor and when it is determined that the SCRtemperature has dropped to a safe level, the microcontroller willautomatically resume operation.

On the bottom of the printed circuit board can be two status LEDs (notshown), preferably one red and one green, that are viewable throughholes in a controller cover. The green LED is lit when themicrocontroller 30 has determined that the voltage level of the ringingpulses is within the desired range, otherwise the red LED is lit. Asingle-pole double-throw relay contact (not shown) is preferablyprovided for remotely monitoring the status—when the green LED is litthe relay is energized.

The functioning of the above-described SCR-switched circuit is asfollows: The SCR (Silicon Controlled Rectifier) acts like a diode with acontrollable turn-on capability. When voltage is applied in the “forwarddirection” (forward-biased-anode positive with respect to cathode) adiode will conduct current. However, the SCR will NOT conduct whenforward-biased unless a current is made to flow in its “gate” circuit.If no gate current is applied, the SCR will “block” the flow of currenteven when forward-biased. Both the SCR and the diode will block the flowof current when the direction of current flow reverses (cathode to anodeis the reverse-current direction). The SCR cannot be turned off byremoving its gate current after it has been turned on. It can only beturned off by reversing the direction of current flow. In this it actsthe same as a silicon diode (rectifier). Hence its name, “siliconcontrolled rectifier”.

With this as background, a normal cycle of the system proceeds asfollows. The coil, transformer and SCR switch are all connected inseries. When the time-varying (50 or 60 cycles per second) transformervoltage applies a forward bias to the SCR, gate current is applied andthe SCR conducts current through the coil. The SCR has a very lowvoltage drop from anode to cathode when conducting (less than or equalto one volt typically) so it acts like an almost-perfect switch. On thecircuit boards of prior devices MOSFETs (Metal-Oxide-Silicon FieldEffect Transistors) are used as the switch, and these MOSFETs have alarger “forward” voltage drop than does an SCR and so dissipate moreheat than the SCR. For this reason, in the prior devices tenparallel-connected MOSFETs are used to carry the coil current, where asingle SCR will do the same job in devices according to the presentinvention with lower overall power loss.

When the coil current attempts to reverse direction, the SCR turns offand allows voltage to rise across it, just as a diode would do. The SCRthen blocks current flow when the current reverses. Because the voltageand current across the coil are almost 90 degrees out of phase with eachother, the current crosses zero (reverses) when there is stillsubstantial voltage across the coil. This frees the coil to “ring” at alow voltage level due to the energy stored in its stray capacitance.

After this initial small or natural “ringing” pulse has died out, asmall current is allowed to build up in the coil by closing a MOSFETswitch. This switch does not carry the main coil current, so a smallswitch can be used for this “recharging” function.

When this current has reached a preset level, the MOSFET is turned off,and the coil voltage “rings” again, this time producing a large ringingpulse at a higher voltage level, depending on the amount of current thatis allowed to build up.

The regulator circuit measures the peak value of this “ringing” voltageand compares it to the desired value, which is stored as a number in themicroprocessor “chip” on the circuit board. If the voltage is too low,then after the ringing pulse has died away the microprocessor turns theMOSFET on again and holds it “on” for a longer time, allowing more coilcurrent to build up than before. The MOSFET is then turned off, and thelarge ringing pulse repeats.

If the pulse voltage is too high, the microprocessor reduces the “ontime” of the MOSFET switch for the next pulse, causing less coil currentto build up. The MOSFET then turns off and the ringing voltage is againmeasured.

When the ringing voltage has reached the desired level (it falls withina “window” range of voltages stored in the microprocessor), theregulator “remembers” this and fixes the MOSFET “on” time for subsequentpulses at this value unless the pulse voltage drifts outside the“window” again. This can occur if the coil resistance changes as thecoil temperature changes during operation. If that occurs, precedingsteps are repeated until the voltage is once again within the “window”.

All the large “ringing” pulses are generated during the interval whenthe SCR switch is reverse-biased by the applied circuit voltage from thepower transformer. The SCR allows the ringing pulses to occur (its gatecurrent is zero during this interval), even though the ringing pulsevoltage will at times cause the SCR voltage to switch over to the“forward” bias condition. The SCR will not turn on when this occurs,unlike a diode, as its gate current is held to zero by the gate driverswitch.

Several large ringing pulses can be inserted in the reverse bias timeinterval. The number of pulses depends on the desired voltage of thepulse, the inductance of the coil, the capacitance in parallel with thecoil (including stray capacitance) and the degree to which each pulse ispermitted to decay. In a first embodiment of the invention, each pulseis allowed to substantially (optionally, fully) decay and, all otherparameters being equal, fewer pulses are produced. In a secondembodiment of the invention, the pulses are not permitted tosubstantially decay prior to the generation of the next pulse; thisallows the generation of a significantly greater number of pulses. Thedifference between these embodiments may be seen by comparing FIGS. 4and 5.

Other techniques can be used to generate ringing pulses similar to thosedescribed above. The preferred technique, as described above, uses thecoil's inductance as an energy storage element to generate the ringingvoltage, so it is a simpler method than others which must store theenergy elsewhere. However, any device that stores the required pulseenergy can be used to generate a ringing pulse. For example, a capacitorcan be charged to 150 volts (or any other desired voltage) and switchedacross the coil during the “off time” of the coil current. This too willgenerate a ringing pulse, but it requires a high voltage power supplyand an extra capacitor. This method also increases the capacitance inthe “ringing” circuit, and causes a lower “ringing” frequency than ourmethod does. The preferred method uses the unavoidable “stray”capacitance of the coil as the resonating capacitance, and generates thehighest possible ringing frequency.

A session testing the performance of a device such as shown by FIG. 1and as described above with a digital scope on a workbench produced theresults shown in FIGS. 2, 3 and 4. As can be seen, the inventive controlcircuit can fit several (in this case six) large ringing pulses into theavailable “off” time window between transformer current pulses. Thenumber of large ringing pulses is selectable by inputting a number tothe control program via the computer programming interface.

FIG. 2 shows a single pulse from the group; the printing at the leftindicates the two horizontal cursor lines were 208 volts apart. Thesweep speed is 100 microseconds (μs)/division. The voltage scale is50V/division.

In FIG. 3 is seen the first “natural” ring when the SCR turns off, about75 volts peak-to-peak. Then come the large rings caused by the controlcircuit. The large ringing pulses are between three and four timeslarger in voltage than the small “natural” ringing pulse. More than onelarge ringing pulse visible in FIG. 3. The sweep speed for this FIG. 3is 200 μs/division and the voltage scale is 50V/division.

In FIG. 4 we see a full six large ringing pulses, each of the pulsesafter the first beginning after the prior pulse has substantiallydecayed. These fit into the approximately 8 millisecond “SCR off” timefor this size (one inch) device. With larger coils, this time may beshorter and fewer pulses will fit in. The sweep speed here is 2ms/division and the voltage scale is 50V/division.

Finally, FIG. 5 shows the result of more than six ringing pulses in anembodiment in which new ringing pulses are initiated before prior pulsessubstantially decay.

As is evident from the foregoing description, one or more large ringingpulses is generated within a time interval defined as a portion of asingle cycle of a 50 or 60 hz AC signal. Thus, each such time intervalhas a duration corresponding to a portion of a cycle of a 50 or 60 hzsignal. Optionally, the one or more large ringing pulses are generatedin intervals defined as portions of successive cycles of the 50 or 60 hzAC signal, in which case the one or more large ringing pulses are saidto occur in successive intervals spaced in a way that corresponds to 50or 60 hz.

The circuit of the switching means illustrated in FIG. 1 is one which isoperable to produce one period of ringing current and ringing voltagefor each alternate half cycle of the applied supply voltage. However, ifdesired, the switching circuit can also be designed to operate in a fullwave mode wherein a period of ringing current and of ringing voltage isproduced for each half cycle of the supply voltage.

In summary, the apparatus and method embodying the present inventionemploys an SCR for handling the main coil current which is responsiblefor the formation of the low frequency electromagnetic field, and uses asingle MOSFET switch to draw a relatively small current through thecurrent coil(s) after the main current pulse has ended. One or morelarge ringing pulse or pulses is then produced by turning this switchoff. Several ringing pulses can be produced in this way during the zerocurrent interval through the coils. The number of pulses which may begenerated depends on the characteristics of the system and whether eachring is allowed to substantially decay (first embodiment) or whethersubsequent rings are generated prior to substantial decay in theprevious ring (second embodiment).

One way to practice this invention is to situate a feed stream inproximity to the coil assembly while ringing pulses are being generated,for example, by flowing the feed stream through the magnetic fluxgenerated by the coil assembly during the ringing pulses. In aparticular embodiment, an apparatus embodying the invention may comprisea pipe unit that includes a pipe through which liquid to be treatedpasses. The pipe may be made of various materials, but as the treatmentof the feed stream effected by the pipe unit involves the passage ofelectromagnetic flux through the walls of the pipe and into the liquidflowing therein, the pipe is preferably made of a non-electricalconducting material to avoid diminution of the amount of flux reachingthe liquid. Other parts of the pipe unit may be contained in or mountedon a generally cylindrical housing surrounding the pipe.

The pipe unit includes one or more electrical coils of a coil assemblyas described herein, surrounding the pipe, with an AC power source andcontrol circuitry connected to the coil assembly as described herein.The number, design and arrangement of the coils making up the coilassembly may vary. In illustrative embodiments, the coil has four coilsections arranged in a fashion similar to that of U.S. Pat. No.5,702,600 and U.S. Pat. No. 6,063,267, the disclosures of which areincorporated herein by reference. The coils are associated withdifferent longitudinal sections of the pipe. That is, a first coilsection is wound onto and along a bobbin and in turn extending along afirst pipe section, a second coil section is wound on and along anotherbobbin itself extending along the a second pipe section, and third andforth coil sections are wound on a third bobbin itself extending along athird pipe section, with the third coil section being wound on top ofthe forth coil section. The winding of the third and forth coil sectionson top of one another, or otherwise in close association with oneanother, produces a winding capacitance between those two coils whichforms all or part of the capacitance of a series resonant circuit in acoil assembly as described herein. Alternatively, the coils may be woundaround the pipe, without the use of a bobbin.

In use, a fluid is passed through the pipe unit, and while the fluidpasses therethrough, the AC power source and control circuitry generatelow frequency electromagnetic fields and ringing pulses in the coil asdescribed herein.

Due to the complexity of the process for producing the ringing pulses,the majority of this specification is devoted to the method and circuitassociated with the generation of the ringing pulse. It should not beconstrued, however, that the process and equipment associated with theringing pulse is of any greater importance than the process andequipment associated with the low frequency electromagnetic field.

As indicated above, the invention can be used with any cross-flowfiltration system. Accordingly, the coils 620, 622 and/or 624 of reverseosmosis system 610 of FIG. 6, and the associated control circuitrytherefor (FIG. 1), may be employed as well for microfiltration,ultrafiltration, and/or nanofiltration.

The terms “first,” “second,” and the like, herein do not denote anyorder, quantity, or importance, but rather are used to distinguish oneelement from another. In addition, the terms “a” and “an” herein do notdenote a limitation of quantity, but rather denote the presence of atleast one of the referenced item.

Although the invention has been described with reference to particularembodiments thereof, it will be understood by one of ordinary skill inthe art, upon a reading and understanding of the foregoing disclosure,that numerous variations and alterations to the disclosed embodimentswill fall within the spirit and scope of this invention and of theappended claims.

1. A cross-flow filtration system comprising: a first filter elementhaving a first conduit for receiving a flow of a first aqueous feedstream, a second conduit operable to discharge a flow of first permeatewater and a third conduit operable to discharge a flow of firstretentate water; a first coil assembly disposed about the first conduitand being operable to subject the first aqueous feed stream to firstelectromagnetic pulses; a second filter element ‘in fluid communicationwith the first filter element via the third conduit and the secondfilter element being operable to receive the first retentate water viathe third conduit; and a second coil assembly disposed about the thirdconduit and being operable to subject the first retentate water tosecond electromagnet pulses.
 2. The cross-flow system of claim 1,wherein at least one of the first coil assembly and the second coilassembly comprises: an AC power source connected with at least one ofthe first coil assembly and the second coil assembly, the AC powersource having a period including a first half-cycle of one polarity anda second half cycle of a polarity opposite to that of the firsthalf-cycle; a first switch connected in series with at least one of thefirst coil assembly and the second coil assembly to form a seriesconnected circuit; a second switch connected with at least one of thefirst coil assembly and the second coil assembly to form a secondcircuit; and control means for the first switch, the control means beingconfigured to close the first switch and open the second switch during afirst half-cycle of the AC power source period and, during a secondhalf-cycle, to perform a subroutine of closing and then opening thesecond switch to produce at least a first large ringing pulse in atleast one of the first coil assembly and the second coil assembly. 3.The cross-flow filtration system of claim 1, wherein the control meanscloses and opens the second switch to produce a second large ringingpulse before the first large ringing pulse substantially decays.
 4. Thecross-flow filtration system of claim 2, wherein the control meanscloses and opens the second switch to produce a second large ringingpulse after the first large ringing pulse substantially decays.
 5. Thecross-flow filtration system of claim 2, wherein said first switch is asilicon controlled rectifier (SCR) forming a first electrical loop withthe AC power source and at least one of the first coil assembly and thesecond coil assembly.
 6. The cross-flow filtration system of claim 5wherein the second switch is electrically connected in parallel with theSCR.
 7. The cross-flow filtration system of claim 5, further comprisinga thermistor affixed to the SCR, wherein the thermistor is connected tothe control means and the control means is configured to halt conductionof current through the SCR when a temperature of the SCR exceeds apredetermined maximum value.
 8. The cross-flow filtration system ofclaim 2, wherein the control means includes an optical relay that whenactivated passes a trigger signal to the gate of the SCR and that whendeactivated removes the trigger signal from the gate of the SCR.
 9. Thecross-flow filtration system of claim 2, wherein the second switch is aMOSFET.
 10. The cross-flow filtration system of claim 2, furthercomprising regulating means for regulating a voltage of the ringingpulse.
 11. The cross-flow filtration system of claim 10, wherein theregulating means includes means for adjusting the voltage of the ringingpulse to lie between a predetermined minimum value and a predeterminedmaximum value.
 12. The cross-flow filtration system of claim 1, whereinat least one of the first the coil assembly and the second coil assemblyis placed circumferentially around the input feed conduit.
 13. Thecross-flow filtration system of claim 1, wherein the second filterelement has a fourth conduit operable to discharge a flow of secondpermeate water and a fifth conduit operable to discharge a flow ofsecond retentate water.
 14. A cross-flow filtration system comprising: afirst filter element having a first conduit for receiving a flow of afirst aqueous feed stream, a second conduit operable to discharge a flowof first permeate water and a third conduit operable to discharge a flowof first retentate water; a first coil assembly disposed about the firstconduit and being operable to subject the first aqueous feed stream tofirst electromagnetic pulses; a second filter element being in fluidcommunication with the first filter element via the third conduit andthe second filter element being operable to receive the first retentatewater via the third conduit, and the second filter element having afourth conduit operable to discharge a flow of second permeate water anda fifth conduit operable to discharge a flow of second retentate water;a third filter element being in fluid communication with the secondfilter element via the fifth conduit and the third filter element beingoperable to receive the second retentate water via the fifth conduit; atleast one additional coil assembly disposed about at least one of thethird conduit and fifth conduit; and the at least one additional coilassembly being operable to at least one of: subject the first retentatewater to second electromagnet pulses; and subject the second retentatewater to third electromagnet pulses.
 15. The cross-flow filtrationsystem of claim 14, wherein the third filter element has a sixth conduitoperable to discharge a flow of third permeate water and a seventhconduit operable to discharge a flow of third retentate water.